well, here are some hints for you guys that I found with a little research..some of the answers have already been mentioned...but I think its important to check your codes FIRST, then have components bench tested, load tested, ect....in that order.
it would seem that the PCM (Post 1996 vehicles only) relays information from your vehicles sensors and makes note of them as temporary problems or repeated problems and sends the codes to your vehicles on board storage system which you can retrieve on your dash board.
I found both OBDII scanner and manual tests for the PCM...
and I quote:
Dodge's powertrain control module (PCM) serves as the central computer for a vehicle's diagnostic system. The PCM analyzes sensor readings and engine functions. As soon as a component within the engine or fueling system malfunctions, the PCM issues a code and labels the problem either "trouble" or "pending." If the PCM were to cease working properly, your Dodge's diagnostic system would become untrustworthy. Testing this valuable device can be accomplished in a few minutes
Prepare some important materials before you check your Dodge's PCM. Consult your OBD-II (on-board diagnostic) scanner's handbook for a list of generic trouble codes. Also, find and print out Chrysler's supplemental OBD-II codes online and print them out. Take a highlighter to both and mark all the trouble codes that deal with the PCM itself. For example, P0601 denotes failure within the PCM itself. While testing the system, you should keep an eye out for it.
Place the coding resources in your Dodge's navigation seat. Then, get into the vehicle's driver's seat.
Locate your Dodge's computer outlet beneath the dashboard. The location of this data link connector depends on year and model of the Dodge. It may be beneath the steering wheel, next to the left kick panel or above the gas pedal.
Connect your OBD-II scanner to your Dodge's computer outlet. Switch the device on, and then turn the Dodge's electrical system on. You may own an OBD-II scanner that requires the engine to be running as well. Always keep in mind that no two scanner brands function exactly the same.
Look at your device's display screen. If there are no codes waiting for you, you own a scanner that is not preset for automatic code retrieval. Locate the procedure for entering a "Code scan" command. It usually entails pressing a button.
Scroll through the codes on the scanner's display screen. The PCM is part of the vehicle's powertrain. So you can safely exclude any OBD-II codes that start with "B," "C" or "U." Reference the source material you previously placed in the navigator's seat and look specifically for codes relating to the PCM's operations.
this also from Just Answer:
What you would need to do is check it's powers and grounds and then make sure there are no shorts on a couple circuits, and if all is ok then the powertrain control module (PCM) can be condemned and replaced.
With your symptoms the PCM is definitely down. That's why the fuel gauge and voltmeter don't work, and you are seeing the bus message because the PCM isn't communicating with other modules on the bus.
I see that you've checked fuses already but it's still best to verify the PCM power feeds. The PCM is the silver module under the hood with three 32-way electrical connectors. Find the black connector and unplug it, turn it over and you will see the terminals are numbered. Find pins 2 and 22, these should both have battery voltage with the key on.
At the same time, also check the two PCM grounds. These are pins 31 and 32 in the same connector. Pin 32 may not be numbered making it look like there are 31 pins in the connector, but 31 and 32 are the last two in the connector.
If all is ok disconnect the throttle position, MAP, cam or crank sensor and check for a short to ground on the orange wire. This is the 5v reference wire and the PCM will go down if it shorts to ground. If it does happen to be shorted then you've got an internally shorted sensor or wiring issue. These are possible but not that common.
If this is ok, plug the PCM back in and turn the key on. At whatever sensor you choose, check for the presence of voltage on the black/light blue wire. This is the sensor ground wire, again a short to voltage here will take the PCM down, and it can be caused by wiring or an internally shorted sensor.
If all is ok yet the PCM isn't awake then the problem is internal and it will need to be replaced.
Read more:
http://www.justanswer.com/dodge/7cyki-dakota-test-engine-control-module-when-turn.html#ixzz40Z96cr7f
I hope this helps out...
JP